Protein-calorie malnutrition is a frequent comorbidity in hospitalized patients and there is evidence that the nutritional status may influence the response to drug treatment, mortality, susceptibility to infections, the patient's functional status, duration of hospital stay and, consequently, overall healthcare costs. The causes of malnutrition are manifold. The underlying disease may in fact lead to an increase in the patient's energy needs, whether or not associated with a reduction in caloric intake. The same therapeutic treatments can further worsen the energy balance without considering that the patient can be kept fasting for the execution of some diagnostic procedures. Therefore, a further deterioration of nutritional status during hospitalization could occur.